Forrest Mims III: S.A. gets a taste of an old-fashioned Texas winter

:
February 14, 2011

The temperature at the Stinson Municipal Airport in San Antonio in early February resembled an old-fashioned Texas winter--a spell of subfreezing weather sandwiched between spring-like days. Data from NOAA and graphic by Forrest M. Mims III.

Young Texans and recent arrivals have been spoiled by the relatively warm winters of recent years. Now they have finally experienced a cold spell reminiscent of those that occurred during old-fashioned Texas winters.

On our place, a thermometer was unnecessary to know that early February was a return to the chilly winters of past decades. There's a livestock tank here, cut from an old water heater, that used to hydrate the sheep we once raised. The frigid weather during the first four days of February transformed the water in that tank into solid ice. The last time that happened was shortly after we arrived a quarter of a century ago.

A string of three sub-freezing days is very rare in South Central Texas, at least since records were begun in San Antonio in 1885. Yet the recent cold snap was not nearly as chilly as some previous record lows in San Antonio.

According to the National Weather Service, the coldest temperature recorded in San Antonio since 1885 was zero on Jan. 31, 1949. The day before, 4.7 inches of snow fell on the city.

Our rural place was supposed to receive up to 3 inches of snow the night of Feb. 3. Weather systems enjoy fooling forecasters, and we received only a quarter inch. The problem for motorists across the region was that the snow fell over a blanket of ice left by freezing rain.

The snow we received fell in the form of graupel instead of flakes. Graupel is white pellets of snow that are softer than the clear pellets of ice that fall as sleet.

The thin coating of snow that blanketed our place provided an unexpected bonus in the form of hundreds of neatly printed animal tracks. Deer and other animals leave their prints behind in moist soil, but nothing beats a thin layer of fresh snow for recording animal activity.

It was amazing to see so many signs of animal life throughout our woods. Especially interesting were the crisp prints left by deer and rabbits only hours or minutes before but whose makers were nowhere to be seen. A deeper snow would not have provided such well-defined tracks.

The snow also provided an opportunity to measure how well it reflects the sun's ultraviolet radiation. I've done this in snow country, but this was the first time here.

At noon, the snow reflected from 40 percent to 50 percent of the UV received from the sun and the blue sky. This explains why people who do not wear sunglasses can experience snow blindness on a sunny winter day.